The disclosure in the applicants New Zealand Provisional Application Number NZ700670 A Method and Apparatus for the Controlled Delivery of Gases, White et al, is expressly incorporated herein by reference.
Putting aside the role of olfaction, the primary function of the nose is to heat and humidify inhaled air as well as trap and remove debris and pathogens. Heat and humidification are provided by blood flow and airway surface liquid (ASL) respectively. The upper mucus layer within the ASL provides a means of entrapping inhaled debris and pathogens which are then transported by the mucociliary transport towards the nasopharynx for disposal by swallowing or expectoration.
All mammals, including man, have two nasal passageways which typically carry a differing apportionment of tidal airflow. Periodic change in inter-nasal airflow apportionment is known as the nasal cycle. In healthy humans, the nose is the preferred entry point for air entering the airways, serving an important role in maintaining airway health by entrapping inhaled pathogens and pollutants as well as heating and humidifying inhaled air. During nasal breathing, the nose recovers around 30% of exhaled heat and water vapour and provides a region for olfaction to occur. The entire conducting airway is lined with an airway surface liquid (ASL) that not only provides the means of entrapment of inhaled pathogens and pollutants, but is also the medium through which heat and water must pass though from the underlying mucosa. While the nasal airways in all healthy mammals, including man, demonstrate the nasal cycle, the physiological reason for this phenomenon has previously not been well understood. Early work by Eccles et al. (1982) proposed that the ‘nasal cycle’ enables cells and glands to rest and recharge. Later work has hinted that the ‘nasal cycle is probably controlling the balance between the fluxes of heat and water vapour required to condition the inspired air and the ability of nasal blood flow and mucus secretion to supply sufficient heat and water to the surface tissue surface.
More recent work has demonstrated that the nasal cycle provides a means by which the anterior conducting airway copes with conflicting ASL hydration states where each passageway alternatively take turns in either predominantly undertaking the air-conditioning with resultant airway drying or a mucus clearance role where the airway surface liquid remains hydrated. Each of these roles requires different airflow conditions, which are provided by differing rates of airflow passing down each airway.
Apart from its functional role in maintaining airway health, change in the nasal cycle phase in the awake state has also been linked to variation in human cognitive performance on verbal and spatial tasks and cognition associated with alternation of cerebral dominance. During sleep, nasal cycle phase has been linked to ultradian sleep rhythms and autonomic and cardiovascular activities. This work has suggested nasal breathing influences brain activity laterality, brain and body blood flows, heart rate and stroke volume, blood pressure, as well as hormone production.
Normally both nasal airways cycle between two airflow states with one passageway experiencing a higher airflow than the other. This cycle is achieved by varying the passageway geometry through activation of mucosal blood capacitance vessels. The un-obstructed airway, termed ‘patent’, passes the majority of the airflow while the other ‘congested’ airway passes a much lower amount. This bias of inter-nasal airflow toward the ‘patent’ side enables the congested airway to maintain a sufficient ASL hydration level so that effective mucociliary transport can occur. It also allows cells and glands on this side to rest and recharge as there is little fluid demand from the ASL to humidify inhaled air on this side.
The patent side however carries the bulk of the heating and humidification duty and in doing so experiences ASL dehydration and subsequent re-wetting during inhalation and exhalation breath phases respectively. This cyclic ASL dehydration/re-wetting not only exposes the mucosa of this airway to repeated drying and high cellular/gland fluid demands, it also disables the mucociliary transport system within this airway. Different airflow rates within each airway channel are achieved by each airway having either a high or low resistance to tidal airflow. This enables the nose to effectively undertake all if its functions despite the contrasting airflow requirements between air-conditioning and filtration of inhaled air. Typically this bias in airflow between nasal airways lasts for a period of time before swapping sides in what is termed ‘the nasal cycle’. The purpose of this cycle is to enable each airway to take its turn in either being ‘congested’ or ‘patent’ through a switch in the nasal cycle.
Normal inter-nasal airflow partitioning is disturbed during nasal breathing of pressurised air or other gases. The disturbance is characterised by the previously ‘patent’ airway becoming more restrictive to airflow while the previously ‘congested airway’ becomes less restrictive. This change disrupts the normal functioning of the nasal cycle by altering the normal inter-nasal airflow partitioning ratio between the two airways. Pressure elicited change in nasal geometry causes a reduction in the apportionment of tidal airflow through the previously ‘patent airway’ and a greater apportionment to occur through the ‘previously congested’ airway. This leads to cyclic ASL drying to occur along both nasal airways during inhalation which disables mucociliary transport and cellular/gland rest and recovery within the nose.
Nasal breathing of pressurised air or other gases, during treatments such as continuous positive air pressure (CPAP), bi-level air positive air pressure (Bi-PAP) and auto-titrating positive air pressure (APAP), are used to treat obstructive sleep apnoea (OSA). Users of this treatment frequently report symptoms associated with airway drying. This occurs as a consequence of the pressure elicited change in airflow partitioning which prevents the previously ‘patent airway’ from experiencing sufficient re-hydration from condensing outflowing air. Mucosal drying can also occur in the previously ‘congested airway’ as it is now forced to conduct a greater airflow during a period where it would normally experience rest and recovery. Re-wetting through condensing exhaled air can occur in just a couple of exhalation breaths that may take approximately 10 seconds. Supplementary humidification is frequently used to relieve these symptoms but does not seem to lead to improved adherence to the breathing therapy, suggesting that the cause of patient dissatisfaction might be more complex than simply a case of airway drying.
Another significant but mostly overlooked factor concerns the neurological interaction occurring between the nose and hypothalamus. The ultradian rhythm regulated by the hypothalamus regulates many aspects of the central and autonomic nervous systems as well as the regulation of hormones and other active or signalling agents. This regulation includes the basic rest-activity cycle (BRAC) and sleep rhythms through regulation. Human performance, cognition and cerebral hemispheric activity have all been found to be influenced by nasal airflow asymmetries. Forced change in the bias of inter-nasal airflow that normally occurs between the ‘patent’ and ‘congested’ airways can be achieved through the blocking of one airway during nasal breathing of ambient air. This disturbance in normal nasal breathing has been found to influence the hypothalamus through change in ultradian rhythms and BRAC cycle.
WO2011141841 describes a system to deliver the pressurized flow of breathable gas to only a first nostril of the subject such that the airway of the subject is pressurized by the pressurized flow of breathable gas through the first nostril.
U.S. Pat. No. 7,114,497 describes a method and system of individually controlling positive airway pressure of a patient's nares.
It is an object of the present invention to actively regulate inter-nasal airflow partitioning during pressurised or ambient nasal breathing to replicate normal inter-nasal airflow partitioning found during ambient pressure breathing.
It is a further object of the present invention to actively regulate the switch of the inter-nasal airflow apportionment occurring between each of the nasal airways and in doing so mimic the change in status of inter-nasal airflow partitioning that occurs during the nasal cycle.
A further object of the present invention is to influence the neurological interactions between brain and nasal airways and thereby alter the regulation of the body's autonomic and sympathetic nervous systems. This airway/brain interaction influences many ultradian cycle activities, including hormone release and the Basic Rest Activity Cycle (BRAC).
It is a further object of the invention to provide a method and apparatus for providing a flow of pressurised gases which goes some way towards overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.
The background discussion (including any potential prior art) is not to be taken as an admission of the common general knowledge.
It is acknowledged that the terms “comprise”, “comprises” and “comprising” may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning—i.e. they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements.